Shaft tool with detachable top

ABSTRACT

A shaft tool for metal cutting machining, includes a cutting portion and a shaft portion. The cutting portion includes a fist part formed with a cutting edge, and a second part formed with an external screw thread. The first and second parts are of one-piece integral construction. The shaft portion includes an internal screw thread to which the external screw thread is removably secured.

BACKGROUND OF THE INVENTION

The present invention relates to a shaft tool with a detachable top formetal cutting machining.

Most rotating cutting tools comprise a shaft portion for fixing the toolin a holder and an operative cutting portion comprising cutting edges ofa hard material such as cemented carbide, different ceramics,polycrystalline diamond and cubic boron nitride. The cemented carbidemay be either coated or uncoated. Usually, the cutting edges consist ofone or more of the edge lines on a cutting insert that is fastened uponand constitutes the active, cutting part of the operative cuttingportion. This cutting insert is often fastened by a screw, the cuttinginsert having a through-hole, through which the screw is introduced. Inother cases the cutting insert is fastened by a clamp or similarfastening or squeezing element; or by soldering or brazing. Althoughthese well-known fastening arrangements function satisfactorily per se,they are all marred by different inconveniences. Thus, screws and clampsmay for instance burst after repeated and/or too strong tightening, orthey may sometimes loosen due to vibrations, which in a best case makesnecessary a retightening but in a worst case may cause a tool breakdown.Moreover, soldering may cause brittleness and micro-cracks due to theheat when soldering, particularly in the soldered seam. Furthermore, adamaged soldered cutting insert cannot be replaced, wherefore the wholetool has to be disposed of, which of course increases costs. A furtherdisadvantage in connection with locking screws is that it istime-consuming to screw and unscrew locking screws for the fastening ofindexable cutting inserts, particularly when there are tens or evenhundreds of cutting inserts to be mounted, demounted or indexed.

Tools that are smaller in volume, such as end mills and drills, areusually made integrally of one single piece, whereby they consist of thesame hard material as the cutting edges. This brings the advantage thatthe boundary layer of a screw joint, a clamp joint, a soldered seam,etc, is avoided. On the other hand, this "entirety solution" entailsthat the expensive and sometimes brittle and heat variation sensiblehard material also is present in tool parts where it would not benecessary, for instance in the shaft portion.

Still further fastening arrangements comprise wedges, draw bars, etc.

One drawback in connection with more bulky and material-demanding rotarycutting tools is that each individual tool requires its ownmaterial-demanding shaft portion, in spite of the fact that this portionis not worn to the same extent as the operative cutting portion.

Thus, a first object of the present invention is to provide a tool whichin first hand is a rotating cutting tool and which comprises a simplestpossible fastening arrangement between the shaft portion of the tool andthe operative cutting portion.

A second object of the present invention is to decrease the materialconsumption when manufacturing the tool.

Still another object of the present invention is to lay the basis of amore flexible and polyvalent tool system.

SUMMARY OF THE INVENTION

These and further objects have been attained in a suprisingly simple wayby a shaft tool for metal cutting machining comprising a cutting portionand a shaft portion. The cutting portion includes a first part formedwith cutting edge, and a second part formed with an external screwthread. The first and second parts are of one-piece integralconstruction. The shaft portion includes an internal screw thread towhich the external screw thread is removably secured.

BRIEF DESCRIPTION OF THE DRAWINGS

For illustrative but non-limiting purposes, an embodiment of theinvention will now be further described in relation to the appendeddrawing. In the drawing are:

FIG. 1 a side view of an end mill according to the present invention,and

FIG. 2 a top view of the end mill according to FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

An end mill according to the invention comprises a top or operativecutting portion 1 and a shaft portion 2. One essential feature of theinvention is that the cutting portion 1 is made of one integral piecewhich thus includes both a part 3 provided with cutting edges and a part4 provided with threads. The form of part 3 is not an essential featureof the present invention. According to the illustrated embodiment, it isformed as a ball end mill, which has helically twisted main cuttingedges 5 and end cutting edges 6 which extend to the rotation axis of thetool. Between each pair of adjacent main cutting edges extends a chipflute 7. Other examples of feasible embodiments of the part 3 providedwith cutting edges is a straight end mill, a side-milling cutter and acylindrical cutter.

Another essential feature of the present invention is that the operativecutting portion 1 comprises the threaded part 4, which is intended to bethreaded into hole 8 in the circular end surface of shaft portion 2,which hole is provided with a corresponding internal thread. The type ofthread as such is not essential for the invention. Thus, the thread part4 and the hole 8 can be made with different types of threads, each onebeing well-known as such, e.g., a V-thread with a triangular basicprofile (for instance a normal metric thread or a so called M-thread),different pipe threads, trapezoid and square threads and also so calledround-threads. The extension of the thread can describe a cylinder butpreferably the thread has a conical extension, as shown in FIG. 1. Theadvantage with a conical thread is of course that the threads can beengaged and disengaged from each other by a short turning, suitably lessthan two revolutions. The thread is suitably continuous anduninterrupted on the basically cylindrical or conical surface, althoughit could also comprise truncated, longitudinally extending portions.

In order to make possible a fastening of the cutting portion 1 in theshaft portion 2 as stable as possible, the two portions are preferablyprovided with radial and/or axial abutment surfaces, suitably with both.The radial abutment surfaces consist of, on one hand, two cylindricalouter envelope surfaces 11 and 12 situated above and underneath,respectively, the thread of the cutting portion, and on the other handof, two cylindrical, inner envelope surfaces 13 and 14 cooperating withthe former and being located in the hole 8, above and underneath thehole thread, respectively. The axial abutment surfaces comprise aring-shaped shoulder 15, and an end surface 16. The shoulder 15 islocated in a radial plane situated between the parts 3 and 4 of thecutting portion. The end surface 16 is disposed on the shaft portion. Itis possible to form the thread part 4 and the hole 8, respectively, withonly one radial abutment surface which then is placed above the thread,i.e., in the position corresponding to surface 11.

In order to avoid an unintended untightening of the threads during useof the tool, the direction of the thread must be the same as thedirection of rotation. According to the illustrated embodiment, the toolshall rotate clock-wise, wherefore the thread part 4 has a right-handthread.

Since the production of such a cutting portion with threads is notpossible by normal form pressing, or at least very complicated, thecutting insert is produced by an injection moulding technique known perse. In the plastic industry, this technique is a usual productiontechnique for the production of different details. A paste consisting ofor containing thermoplastic or thermo-setting polymers is heated to asuitable temperature and is then pressed through a die into a mould ofdesired geometry. In the powder metallurgy, injection moulding is usedfor the production of relatively complex details of metallic powder,such as cemented carbide powder. The cemented carbide powder is thenmixed with polymers. After moulding, the polymer is removed, whereafterthe detail is sintered in substantially the same way as forcorresponding tool-pressed details.

In order to simplify the screwing and unscrewing, respectively, of thecutting portion 1 in the hole 8, the former has been provided with ashort cylindrical intermediate portion 9 between the cuttingedge-provided part 3 and the thread part 4, the portion 9 having one ormore recesses 10 intended to function as key grips for tightening anduntightening, respectively, of the cutting portion 1 by a suitable key.

Suitably, the shaft portion 2 is made of steel such as tool steel.

By the construction as described above, a number of adavantages havebeen attained. Thus, different threaded tops 1 can be replaced easilyand quickly without detaching the shaft portion 2 out of its holder orout of the milling machine, e.g., from a straight end mill to a ball endmill, or from one diameter to another. Moreover, no further extradetails as in the previously known technique are necessary, such asscrews, clamps, wedges, draw bars, etc. Nor are any irreversiblesoldered seams necessary.

We claim:
 1. A shaft tool for metal cutting machining, comprising acutting portion and a shaft portion removably interconnected; thecutting portion including a fist part formed with a cutting edge, and asecond part formed with a continuous uninterrupted external conicalscrew thread; the first and second parts being of one-piece integralconstruction and injection molded of cemented carbide; the shaft portionincluding an internal conical screw thread to which the external screwthread is removably secured; the cutting portion and shaft portionincluding mutually engageable radial abutment surfaces, separate fromthe screw threads, for positioning the cutting portion and shaft portionrelative to one another in a radial direction with reference to alongitudinal axis of the tool; the radial abutment surfaces includingfirst cylindrical abutment surfaces disposed at axial ends,respectively, of the external screw thread, and second cylindricalabutment surfaces disposed at axial ends, respectively, of the internalscrew thread; the first cylindrical abutment surfaces engagingrespective ones of the second cylindrical abutment surfaces; the cuttingportion and the shaft portion including mutually engageable axialabutment surfaces for limiting axial convergence of the cutting portionand shaft portion.
 2. The shaft tool according to claim 1, wherein thecutting portion and shaft portion include mutually engageable radialabutment surfaces, separate from the screw threads, for positioning thecutting portion and shaft portion relative to one another in a radialdirection with reference to a longitudinal axis of the tool; the cuttingportion and shaft portion including mutually engageable axial abutmentsurfaces for limiting axial convergence of the cutting portion and shaftportion.
 3. The shaft tool according to claim 2, wherein the cuttingportion includes cylindrical abutment surfaces disposed at axial ends,respectively, of the external screw thread; the shaft portion includingcylindrical abutment surfaces disposed at axial ends, respectively, ofthe internal screw thread; the cylindrical abutment surfaces of thecutting portion engaging respective ones of the cylindrical abutmentsurfaces of the shaft portion.
 4. The shaft tool according to claim 2,wherein the internal and external screw threads are of generally conicalconfiguration.
 5. The shaft tool according to claim 4, wherein thecutting portion includes circumferentially spaced recesses for receivinga turning key.
 6. The shaft tool according to claim 1, wherein theinternal and external screw threads are of generally conicalconfiguration.
 7. The shaft tool according to claim 1, wherein thecutting portion includes circumferentially spaced recesses for receivinga turning key.
 8. The shaft tool according to claim 1, wherein thecutting portion comprises a ball end mill.
 9. The shaft tool accordingto claim 1 wherein the first part includes a convex end surface on whichthe cutting edge is disposed, the end surface being intersected by alongitudinal axis of the tool.